The present invention relates to a thermal-transfer printer for recording information by using a ribbon cassette in which a repeatedly usable ink ribbon is wound on a pair of reels.
As is generally known, the ribbon cassettes used in thermal-transfer printers are no longer unusable once the ink has been transferred thermally from the ribbon to the paper. Therefore, the thermal-transfer printers using the cassettes of this type have a device for rotating one of the reels of the cassette to take up the used portion of the ribbon. The other reel can rotate freely. The printers generally comprise a carriage which can reciprocate along a platen, and a thermal head mounted on the carriage. While the carriage is moving in a predetermined direction, the head is heated and thermally transfers the ink from the ribbon to the printing paper, thus printing one line. In doing this, the ink ribbon is fed in the opposite direction to the aforesaid predetermined direction lest it move relatively to the paper. For this purpose, one of the paired reels is rotated by a drive mechanism provided in the carriage. When the printing of the one line ends, the thermal head is deenergized and separated from the paper. Then, the carriage is moved in the aforesaid opposite direction to be returned to a print start position. Thereafter, the head, along with the carriage, is moved in the predetermined direction for printing of another line while the ribbon is being transported in the opposite direction.
Meanwhile, conventional ink ribbons can be used only once since the ink is entirely transferred to the paper in a single printing operation. Therefore, the ribbon need not be rewound for reuse; it is transported only in one direction as aforesaid.
Recently, there have been developed ink ribbons which are coated with thicker ink film for repeated use, 10 to 20 times. When a ribbon cassette including one such ink ribbon is used in the aforementioned prior art printers, the ribbon wound on one reel must be temporarily rewound on the other, or the cassette must be turned over to relocate the reels every time the entire ribbon has been used for printing. This requires troublesome manual work. Moreover, at the end of printing of every line the thermal head must be returned to the print start position to print the next line. Accordingly, it takes a lot of time to print a multitude of lines.
To cope with this, the thermal head may be energized for printing also during the return of the carriage to the print start position so that the portion of the ink ribbon used to print one line is used also in printing the next line. This operation should be able to be repeated until the frequency limit of repeated use of the same portion of the ribbon is reached. In this case, however, the uses of the ribbon must be counted and memorized, complicating the control of the printer. Moreover, when the printer is disconnected from the power supply before the aforesaid frequency limit is reached, and thereafter the printer is connected to the power supply, the printer must be controlled such that the ribbon is not used beyond the remaining frequency limit. In general, therefore, the printer requires a complicated control circuit and sophisticated control program. Even though the printing time is shortened as a whole, the used portion of the ink ribbon, in the case of continuous printing of a multitude of lines, must be taken up at a stroke when the repeatedly used ribbon portion reaches the frequency limit of use. Thus, the printing operation would often be interrupted for a long time, losing its continuity.